1. Field of the Invention
The present invention relates generally to the field of limiting the dynamic amplitude range of bipolar signal voltages and, more specifically, to peak limiting of these signals.
More particularly, the present invention relates to a method of and apparatus for maintaining the peak amplitude of a varying bipolar signal voltage below a predetermined threshold level. The method uses the technique of processing the signal voltages in discrete half-waves, and the apparatus uses a multiple section delay means.
2. Description of the Prior Art
Devices and techniques for limiting the dynamic range of signals are, of course, well known in the signal processing art and are typically needed to avoid exceeding the maximum allowable input signal voltage of one or more signal processing stages in a chain. Most conventionally, an amplifier having a logarithmic amplitude response, or a brute force hard limiter stage is used to keep the peaks of varying signal voltages from exceeding predetermined levels. Both of these methods have advantages of simplicity to offset, in part, the significant signal degradation they cause.
An ideal peak limiter would employ more graceful techniques. A significant improvement would employ an AGC type of action, which is only brought into play by some form of a priori knowledge of the signal amplitudes to be processed. Thus, an ideal AGC peak limiter would be kept out of the signal path when not needed, and would be inserted to perform a non-catastrophic peak signal limiting action only when needed. The prior art efforts to implement an approximation to this ideal peak limiter typically use a delay means of some form to introduce a delay into the signal channel while a parallel control channel makes some decisions as to the signal levels, etc. The control channel then begins to operate on the delayed signal as it emerges. U.S. Pat. No. 3,611,383 to Bar discloses a basic approach along these lines to operate on a unidirectional pulse of a Loran system to keep the received master and slave of sensibly constant amplitude and as free as possible from distortion. Of particular interest in Bar is the use of a delay line of predetermined, fixed delay time corresponding to the known pulse durations and interpulse intervals. The technique is obviously applicable only when the incoming signal has very well known time characteristics. U.S. Pat. No. 3,652,944 to Querry also discloses a delay line/AGC technique for normalizing the amplitudes of undirectional pulse trains. While the prior art teachings of peak limiting of varying signal voltages show that a good deal of effort has been directed to the problem, it is clear that there is significant room for improved techniques, especially in the areas of peak limiting of bipolar signal voltages having wide frequency and amplitude dynamic ranges.